CHAPTER 29 – THE SENSES

Sensory ReceptionSensory Reception

• Sensation - awareness of sensory stimuli (chemicals, light, muscle tension, sounds, electricity, cold, heat, touch)

- sensory info reaches our CNS in the form of action potentials

- sensations result when brain integrates new info

Sect 29.1

•perception - meaningful interpretation or conscious understanding of sensory data - integrates new info w/other sensations & memories

p. 590: What is the picture?

Conversion of Stimuli•Sensory transduction - stimulus

detection means that a cell converts one type of signal into an electrical signal

--What is this electrical signal called?

action potential

- the conversion produces electrical signals called receptor potentials (electrical signals can be weak or strong) *fig 29.2A

Sect 29.2

- action potentials are transmitted to CNS for processing

How is it transmitted?

- brain distinguishes different types of stimuli: so for every stimulus, there is an action potential

- strength of stimulus alters the rate of action potential transmission (the stronger the stimulus, the more action potentials) *fig 29.2B

sensory neurons

•Sensory neurons become less sensitive when stimulated repeatedly - known as sensory adaptation (like wearing braces, eating chocolate then drinking a coke)

- sensory adaptation keeps normal background stimuli at bay

5 TYPES OF RECEPTOR CELLSSect 29.3

5 TYPES OF RECEPTORS1.Pain Receptors - sense dangerous stimuli - make us aware of injury or disease - have pain receptors in all parts of the body except brain (heart defers pain) - pain dendrites are naked as well as hair dendrites

OUCH!!!

2. Thermoreceptors - in skin to detect heat & cold - others monitor temp. of blood - hypothalamus3. Mechanoreceptors - respond to various forms of mechanical energy such as touch and pressure, stretching of muscles, motion, sound - receptors that detect light touch & strong pressure

- stretch receptors monitor position of body parts

- hair cells (such as ear for sound, head & arm for air) detect sound waves & other forms of movement in air & water

- skin contains 3 different receptors: pain, thermo, mechano

4. Chemoreceptors - respond to chemicals in external environment or body fluids- include sensory receptors in nose & taste buds

What part of the body detects this [ ] difference?

- osmoregulators in brain detect changes in total solute [ ] of blood ([ ] of alcohol)

5. Electromagnetic Receptors - respond to electricity, magnetism, & light

- most common type of these receptors is called photoreceptors (including our eyes); these detect visible light

Parts of the EyeSect 29.5

•Sclera - tough, whitish layer of connective tissue that covers the eye

- surrounds the choroid (thin pigmented layer)

- if at the front of the eye, it is transparent & lets light in (cornea)

•Conjunctiva - thin mucous membrane that keeps the eye moist; lines the inside of the eyelids & covers the front of the eyeball, except the cornea- pink eye, nondescriptive conjunctivitis

•iris - choroid at the front of the eye (gives the eye color)- absorbs light rays & prevents them from reflecting w/in the eyeball & blurring vision

- muscles of the iris regulate the size of the pupil

- pupil lets the light into the interior of the eye

•Light then passes through a disk-like lens, which is held in position by ligaments.

•Lens focuses images into the retina, a layer just inside the choroid

- photoreceptors on the retina transduce energy & then action potentials pass via sensory neurons in the optic nerve to the visual centers in the brain

- fovea: photoreceptors that are highly concentrated at the retina’s center of focus

-no photoreceptors in the optic nerve, so the place where the optic nerve passes through the back of the eye is called the blind spot-Blind Spot Link

- although transparent, the lens is composed of hundreds of cells arranged in layers like an onion

2 chambers make up the bulk of the eye: Vitreous & Aqueous Humors• Large chamber

behind the lens is filled w/jelly-like substance

• Much smaller chamber in front of lens is full of liquid similar to blood plasma

• fluid circulates through this chamber

• blockage of the ducts that drain this chamber can lead to glaucoma

•Humors help maintain the shape of the eyeball

Focusing•Muscles attached to choroid

control shape of the lens•when eye focuses on a nearby

object, muscles contract - this constricts the area around the

lens & makes the ligaments that suspend the lens slacken

Sect 29.6

-lens becomes thicker & rounder-when eye focuses on a distant object, muscles will relax & the lens flattens

*This process is called accommodation.

Fig 29.6

•Visual acuity –

ability to read

fine details

(tested w/letters

on a special

chart)

Sect 29.7

Most common visual problems:

*nearsighted - cannot focus well on distant objects

(Focal point occurs before the retinal wall.)

(Near objects focused,… objects further away are blurry.)

*farsighted - cannot focus at short distances

(Focal point occurs beyond retina.)

*astigmatismastigmatism - blurred vision where light rays do not focus at any one point on the retina (usually caused by a misshaped cornea)

Photoreceptors•Photoreceptor cells on retina are

called rods & cones

Sect 29.8

1. Rods - rods are very sensitive to light & enable us to see in dim light at night (shades of gray, movement) - found at edges of retina (about 125 million in humans)

- best night vision is achieved by looking at things out of “ the corner of your eye”

- completely absent from center of focus (fovea)

2. Cones

- cones are stimulated by bright light (distinguishes color, visual acuity)

- found densest in center of visual field (about 6 million in humans)

- 3 types of cones distinguish 3 predominant wavelengths (primary colors)

- groups of cones then distinguish tints

- best vision is looking directly at the object

•rods & cones contain light absorbing visual pigments

- rods = rhodopsin: (absorbs dim light)

- cones = photopsin: (absorbs bright, colored light)

•Rods & cones are stimulus transducers to produce our vision

•process of vision involves 3 different reactions

- eye must form a light image on retina

- image is converted into signals of action potentials via optic nerve

- brain must interpret those sensations to create sight

Hearing & BalanceThe Human Ear

•Outer ear - consists of a flap-like pinna & the auditory canal

- these structures collect sound waves & channel them to the eardrum

- eardrum transmits sound waves to middle ear

Sect 29.9

•Middle ear picks up sound waves from eardrum: 3 little bones are set into motion

- malleus: hammer

- incus: anvil

- stapes: stirrup

- bones vibrate & transmit sound into inner ear through the oval window (membrane covered hole in skull) by producing pressure waves in fluid

•Eustachian tube conducts air between middle ear & back of throat, equalizing pressure

•Inner ear consists of several channels of fluid wrapped in a spiral & encased in bones of skull

INNER EAR,…-cochlea: long coiled tube that contains the actual hearing organ-organ of Corti: long, thin spiral w/in middle of cochlea which is the actual hearing organ-semicircular canals: organ for balance & equilibrium

Process of Hearing•Sound waves at different

pressures vibrate eardrum•middle ear bones are set in motion•bones amplify (about 20x) &

transmit sound to fluid of cochlea through oval window

•cochlea transduces sound waves into action potentials

•Movement of hair cells of the organ of Corti against the overlying shelf of tissue triggers nerve signals to the brain

-louder sounds cause greater movement & more action potentials (sustained loud noises cause damage to hair cells)

-sounds of different pitches stimulate hair cells in different parts of the cochlea (which ever is stimulated sends the action potentials)

- humans hear 20-20,000 Hz

(1 Hertz = 1 vibration per second)

- dogs up to 40,000 Hz

- bats up to 100,000 Hz

Balance•We have 2 sets of balance or

equilibrium receptors (1 on each side)

•each set lies next to the cochlea in 5 fluid spaces

- 3 semicircular canals - 2 chambers (utricle & saccule)•all equilibrium structures operate on

the same principle - bending of hairs on the hair cells

Sect 29.10

•Semicircular canals detect changes in the head’s rate of rotation or angular movement (motion: pitch, yaw, roll)

•clusters of hair cells in the utricle & saccule detect position of ear w/respect to gravity

•conflicting signals from inner ear & eyes may cause motion sickness

Taste•Also known as gustation•taste receptors (chemoreceptors)

are organized into taste buds on our tongue that detect chemicals (through contact)

•5 types: sweet, sour, salty, bitter, umani (meat)

•taste buds respond to specific shapes of molecules

Sect 29.12

Smell• Also known as olfaction• airborne molecules are trapped in mucus• chemoreceptors in upper portion of the

nasal cavity detect airborne molecules & bind w/ receptors

• able to distinguish about 50 general types of odor

• olfaction is tied to limbic system, which is why it’s especially useful at recalling emotions & memories